Engine systems may utilize recirculation of exhaust gas from an engine exhaust system to an engine intake system (intake passage), a process referred to as exhaust gas recirculation (EGR), to reduce regulated emissions and improve fuel economy. An EGR system, such as a low-pressure EGR system, may include various sensors to measure and/or control the EGR. As one example, an engine intake system may include an intake gas constituent sensor, such as an oxygen sensor, which may be employed during non-EGR conditions to determine the oxygen content of fresh intake air. During EGR conditions, the sensor may be used to infer EGR based on a change in oxygen concentration due to addition of EGR as a diluent. One example of such an intake oxygen sensor is shown by Matsubara et al. in U.S. Pat. No. 6,742,379. However, the accuracy of EGR estimates using the intake oxygen sensor may be reduced during certain engine operating conditions (e.g., when the engine is boosted or when purge is enabled and hydrocarbons are flowing through the intake system). EGR flow may also be estimated using alternate EGR sensors. For example, the EGR system may also include differential pressure (DP) sensor positioned around an EGR valve for estimating EGR flow based on a pressure difference across the EGR valve and a flow area of the EGR valve. EGR flow estimates may then be used to adjust a position of the EGR valve and therefore adjust an amount of EGR provided to the engine. Thus, both the IAO2 sensor and the DP sensor may be used to give independent estimates of the EGR flow. However, the inventors herein have recognized that the accuracies of each of the IAO2 and DP sensors may change depending on the engine operating conditions, thereby altering the accuracy of the resulting EGR flow estimates. Thus, under certain engine operating conditions the DP sensor may be more accurate than the IAO2 sensor and vice versa. As one example, the DP sensor may be more accurate than the IAO2 sensor when purge and/or PCV gasses are flowing through the intake system.
In one example, the issues described above may be addressed by a method for adjusting engine operation based on a final gas flow parameter estimate, the final gas flow parameter estimate based on each of a first gas flow parameter estimated with a first sensor, a second gas flow parameter estimated with a second sensor positioned away from the first sensor in a gas passage of the engine, and accuracy values of each of the first and second gas flow parameters. In this way, the final gas flow parameter estimate may have an increased accuracy, thereby improving engine control.
As one example, the final gas flow parameter estimate may be a final exhaust gas recirculation (EGR) flow estimate. For example, an engine may include an EGR passage routing EGR via an EGR valve from an exhaust passage to an intake passage of the engine. An engine controller may estimate a first EGR flow based on a pressure difference across the EGR valve and a flow area of the EGR valve. The engine controller may also estimate a second EGR flow based on an output of an intake oxygen sensor positioned in the intake passage, downstream from the EGR passage. Additionally, the engine controller may assign a first accuracy value to the first EGR flow estimate and a second accuracy value to the second EGR flow estimate based on engine operating conditions during the estimation. For example, the first accuracy value may be based on one or more of compressor surge, a position of a compressor bypass valve, and a differential pressure output by the differential pressure sensor and the second accuracy value may be based on one or more of a status of the intake oxygen sensor, purge flow, and positive crankcase ventilation (PCV) flow. A final EGR flow estimate may then be determined based on the first EGR flow estimate, second EGR flow estimate, first accuracy value, and second accuracy value. For example, the final EGR flow estimate may be more heavily based on one or the first or second EGR flow estimate based on the first and second accuracy values relative to one another. In this way, a more accurate EGR flow estimate may be determined. The engine controller may then adjust the EGR valve in order to deliver the requested EGR flow based on the final EGR flow estimate.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.